1. Field of the Invention
The present invention relates to synchronous adaptation between networks, and more particularly, to a method for reassigning channels during the transmission of IEEE-1394 isochronous data to an external synchronous network between the IEEE-1394 network and an external synchronous network and an apparatus therefor.
2. Description of the Related Art
At the present time, there are various digital devices such as a digital TV (DTV), a digital video camera (DVC), a digital versatile disk player (DVDP), a digital set-top box, etc. The IEEE-1394 standard approved by the IEEE committee is attracting attention as a digital network interface to establish a network with such devices. The network for connecting a DTV, a DVCR, a DVDP, a digital set-top box, etc. to each other using the IEEE-1394 standard is currently established by only the 1394 bus.
However, the synchronous adaptation of the IEEE-1394 network to an external network such as an asynchronous transfer mode (ATM) network and a public switched telephone network (PSTN) is essential for a home network or small office home office (SOHO) environment. In the synchronous adaptation to an external network, the IEEE-1394 network is different from other networks in various aspects, which makes synchronization among networks, which is basic to the adaptation of one network to another, difficult to perform.
FIG. 1 schematically shows a network connected by the IEEE-1394 bus. Referring to FIG. 1, various digital devices 100 through 106 are connected to each other by the IEEE-1394 bus at home. The Internet service is performed from the outside to the various digital devices through Ethernet. However, since such a constitution has no reliability with respect to time, the constitution is not suitable for the real-time transmission of data and has no concept of synchronization.
FIG. 2 schematically shows an ATM network. Two Central ATM switching systems 200 and 202 of a core network denote a network node interface (NNI) between central telephone offices. ATM switching systems 204 and 206 denote a user network interface (UNI) between subscribers 208 and 210 and the NNI.
FIG. 3 schematically shows a PSTN. A case where a TDX switching system 302 of the central telephone office is connected to a home network 304 through a telephone line and a case where the TDX switching system 302 is connected to a SOHO network 305 through a leased line are shown.
These networks currently operate independently. The adaptation of the home network or SOHO network environment connected by the IEEE-1394 bus to the external network will be performed hereafter. However, the ATM network and the PSTN which are external networks are fundamentally different from the IEEE-1394 network in the transmission of isochronous data, which makes the synchronization among the networks which is basic to the adaptation of one network to another, difficult to perform. There is no solution to the synchronization of the IEEE-1394 network with the external network.
In a current situation where the respective networks shown in FIGS. 1 through 3 are constituted, the Internet service is provided by the synchronous adaptation of the IEEE-1394 network to the Ethernet. However, since the adaptation of the IEEE-1394 network to the Ethernet has no concept of synchronization and the transmission of the IEEE-1394 isochronous data is not guaranteed as mentioned above, it is not possible to provide a real time service.
Meanwhile, in the case of the ATM adaptation layer 1 (AAL1) method of the ATM or the time division multiplexing (TDM) method of the PSTN, the synchronization is performed at uniform time intervals and real time speech and data services are guaranteed. Also, data is uniformly transmitted in the order of assigned channels. However, in the case of the IEEE-1394 network, a synchronous signal should be generally generated at 125 xcexcs intervals. However, it is not possible to guarantee the 125 xcexcs intervals due to the influence of asynchronous transmission. Namely, a cycle start packet which is a synchronous signal can be delayed more than 125 xcexcs and transmitted. Also, the order of the transmitted data channels cannot be guaranteed to be uniform unlike the ATM or the PSTN.
As the IEEE-1394 network becomes the solution of the home network and the SOHO network, the adaptation of the IEEE-1394 network to the ATM network or the adaptation of the IEEE-1394 network to the PSTN is essential. Therefore, the problem of synchronization among the networks which is basic to the adaptation of one network to another should be solved.
To solve the above problem, it is an object of the present invention to provide a method for reassigning channels during the transmission of the IEEE-1394 isochronous data to a synchronous network by which it is possible to perform synchronization among networks by overcoming the differences between the IEEE-1394 network and other networks.
It is another object of the present invention to provide an apparatus for reassigning channels during the transmission of the IEEE-1394 isochronous data to the synchronous network.
Accordingly, to achieve the first object, there is provided a method for reassigning channels during the transmission of isochronous data from the IEEE-1394 network to an external synchronous network, comprising the steps of (a) forming a mapping table showing the relationship between the channels of the IEEE-1394 network and the channels of the external synchronous network when a call is set with respect to the external synchronous network, (b) reading the channel order from the header of the isochronous data to be transmitted, (c) reassigning the channel order of the IEEE-1394 network according to the channel order of the external synchronous network with reference to the mapping table, and (d) transmitting the isochronous data to the external synchronous network according to the reassigned channel order.
To achieve the second object, there is provided an apparatus for reassigning channels during the transmission of isochronous data from the IEEE-1394 network to an external synchronous network, comprising a memory for sequentially storing the isochronous data to be transmitted and storing a mapping table showing the relationship between the channels of the IEEE-1394 network and the channels of the external synchronous network, a logic unit for forming the mapping table when the isochronous data is stored in the memory and reassigning the channel order of the IEEE-1394 network according to the channel order of the external synchronous network with reference to the mapping table, and a controller for controlling the operation of the logic unit and transmitting the isochronous data stored in the memory according the reassigned channel order when the channel order of the IEEE-1394 network is reassigned by the logic unit.